Add documentation examples for consider-using-join. (#6637)

Co-authored-by: Pierre Sassoulas <[email protected]>

Author: mbyrnepr2

doc/data/messages/c/consider-using-join/bad.py

@@ -0,0 +1,7 @@
+def fruits_to_string(fruits):
+    formatted_fruit = ""
+    for fruit in fruits:
+        formatted_fruit += fruit  # [consider-using-join]
+    return formatted_fruit
+
+print(fruits_to_string(["apple", "pear", "peach"]))

doc/data/messages/c/consider-using-join/good.py

@@ -0,0 +1 @@
+print("".join(["apple", "pear", "peach"]))